1. Field of the Invention
The present invention relates to a copying apparatus, more particularly, having a sorter so that sheets having images transcribed by a copying machine can be distributed and stapled accordingly after being ejected from the copying machine.
2. Description of the Related Art
Recently, responding to the increasing demand for automatized paper handling system for the copying machines, the optional systems such as the automatic document feeding system and the sorting system designed for sorting or grouping copied sheets have been developed and commercialized in various types one after another. The users of the copying machines are now requiring the sorter-finisher system capable of automatically binding and stacking sheets which have been distributed in the sorting system, and this type sorter-finisher system has already been commercialized for some of large-sized copying machines.
For a simple sorter, a movable bin type sorter is conventionally proposed, wherein a plurality of bins stacked in the vertical direction can independently move and, at the same time, each space between bins can be widened, whereby sheets are distributed and sorted into the bins sequentially from the top bin to the bottom bin. Incidentally, when such a movable bin type sorter is provided with a sheet stapling function, the bins are so arranged to be able to move sequentially from the bottom bin to a sheet take-out position, where sheets are then delivered to a stapling unit. Therefore, since the sheets are distributed and sorted into the bins sequentially from the top bin, lower bins having no stored sheets need to be moved at first to the sheet take-out position, as in the case of a stapling operation, whereby much lost time occurs.
In contrast, with a sorter having a sheet stapling function, when a non-sorting mode is selected as an operation mode and when the number of copy sets is set to more than 2, sheets having the same image formed thereon are stored into the same bin. In this case, if the stapling mode is selected to execute the stapling operation, the sheets having the same image formed thereon are pointlessly stapled.
Further, with this type of sorter, when the sheet size for the copying operation is changed during the copying operation in the stapling mode, the correct stapling operation for different sizes of sheets is impossible even if the change of sheet size is acceptable for the stapling operation. Therefore, when moving to the stapling operation, sheets are poorly stapled.
Furthermore, there is a possibility that an operator may erroneously select the stapling mode when initially designating an operation mode. In this case, if the operator realizes that a mistake has been made in the sorting operation, the operator may stop the copying operation. However, such a procedure is cumbersome, causing much inconvenience. Additionally, when the stapling mode is selected and when any sheets remain in a stack tray, the remaining sheets and other newly-stapled sheets are mixed with each other and exceed the capacity of the stack tray, thereby disadvantageously causing sheets to be jammed and poorly stored.
With the above-mentioned sorter, sheets distributed and stored in each bin need to be taken out and delivered to the stapling unit. For example, as a well-known sheet take-out mechanism, a mechanism for taking out sheets distributed and stored in each bin, catching them with pivotal arms and a mechanism for feeding sheets to a stapling unit with a feeder are disclosed in U.S. Pat. Nos. 4,361,393 and 4,248,525. However, such a pivotal arm type or a feeder type sorter becomes mechanically complicated and large-sized, and is not applicable to a small-size copying apparatus for general users.
Therefore, the inventors of the present invention have thought of a mechanism, wherein each bin having sheets distributed and stored therein is lowered sloping down to a sheet take-out position so that the sheets slide down out of the bin to a transport unit for transporting the sheets to a stapling unit due of their own weight, whereby the sheets are positively fed to the transport unit through pinch roller pairs for taking out sheets. However, this mechanism has a problem in that the alignment of sheets is disturbed unless the pinch roller pairs timely catch the sheets.
On the other hand, in order to transport a plurality of piled sheets from one tray to another tracing an almost arcform curve, as a well-known method, an arcform transport path is constituted of guide plates and a plurality of roller pairs are disposed to have the transport path between each pair of them, whereby sheets are subjected to a transporting force. In this case, any pair of rollers facing each other rotates at the same peripheral velocity. However, with the sheet transport apparatus, due to the arcform transport path, the distance for sheets passing outside the path is little longer than that of sheets passing inside the same path. When inside rollers and outside rollers rotate at the same peripheral velocity as mentioned above, the sheets passing outside the path reach an outlet of the path later than the sheets passing inside the same path. Therefore, when the outside sheets fall from the outlet onto a tray, the inside sheets having already left the path act, as a load, on the outside sheets going out later, thereby diadvantageously disturbing the alignment of the sheets on the tray and causing the outside sheets to be jammed between the guide plates.